Infantry is a specialization of military personnel who engage in warfare combat. Infantry generally consists of light infantry, irregular infantry, heavy infantry, mountain infantry, motorized infantry, mechanized infantry, airborne infantry, air assault infantry, and naval infantry. Other types of infantry, such as line infantry and mounted infantry, were once commonplace but fell out of favor in the 1800s with the invention of more accurate and powerful weapons.

Air assault is the movement of ground-based military forces by vertical take-off and landing (VTOL) aircraft, such as helicopters, to seize and hold key terrain that has not been fully secured, and to directly engage enemy forces behind enemy lines. In addition to regular infantry training, air-assault units usually receive training in rappelling, fast-roping techniques, and air transportation. Their equipment is sometimes designed or field-modified to allow better transportation and/or carrying within aircraft.